1. Field of the Invention
The present invention generally relates to electronic component packages. More specifically, the present invention relates to the structure of a package of an electronic component such as a compound semiconductor which is used to transmit signals with a high transmission rate and requires a sealed environment.
2. Description of the Related Art
Compound semiconductors ICs such as GaAs (gallium arsenide) or InP (indium phosphide) having high frequency properties are used for optical transceivers or the like. In order to prevent degradation with time due to corrosion of an IC or wiring, the compound semiconductor is packaged by metal, ceramic, or the like to ensure sealability. In addition, in the high frequency IC package, if the resin or the like comes in contact with the connection part or the surface of the IC, the high frequency properties may become degraded. Therefore, it is general practice to apply a cavity structure to the high frequency IC package.
FIG. 1 through FIG. 3 are schematic views showing first through third related art examples of a driver IC package having a compound semiconductor IC and an optical component.
In the first example shown in FIG. 1 in the related art, a driver IC package 1 having a compound semiconductor IC and an optical component 7 are connected to each other by a coaxial cable 503. Furthermore, in an example shown in FIG. 2 in the related art, a printed wiring board 6 having a main surface where a high frequency device 5 is mounted and an optical component 7 are connected to each other by a wire 8 made of gold (Au). In an example shown in FIG. 3, the printed wiring board 6 having the main surface where the high frequency device 5 is mounted and the optical component 7 are connected to each other by leads 9 made of metal.
On the other hand, in a module such as the optical transceiver where such as the driver IC package 1 or the high frequency device 5 is used, accelerating of transmitted signals, miniaturization of the module, and low manufacturing cost are required.
However, since the coaxial cable 503 is used in the example shown in FIG. 1, it is difficult to achieve the miniaturization of a portion where the coaxial cable 503 is used. In addition, since an internal circuit of the IC package and the coaxial cable should be connected to each other while sealing is ensured, the manufacturing cost of the entire package is increased.
In addition, in the second and third examples shown in FIG. 2 and FIG. 3, respectively, the gold (Au) wire 8 or the leads 9 are used. However, in the case of the gold (Au) wire 8 or the leads 9, impedance is mismatched so that the high frequency properties may be degraded. It is general practice that the properties are influenced if the length of the impedance mismatching part exceeds approximately one twentieth ( 1/20) of a wavelength. For example, in a case of 40 GHz, it is preferable that the length of the gold (Au) wire 8 or the lead 9 be equal to or less than 0.37 mm. Because of this, in the high frequency case, it is difficult to cancel (compensate for) the position shift of the printed wiring board 6 and the optical component 7 so as to connect the printed wiring board 6 and the optical component 7 to each other by the gold (Au) wire 8 or the leads 9.
Because of this, recently, an example shown in FIG. 4 has been suggested. FIG. 4 is a schematic view showing a first related art example of the driver IC package having the compound semiconductor IC and the optical component connected by a flexible board.
In the example shown in FIG. 4, the printed wiring board 6 having the main surface where the high frequency device 5 shown in FIG. 2 and an optical device 27 are connected to each other by a flexible board 504 so that high frequency signal lines are connected to each other. The flexible board 504 is made of, for example, polyimide so that impedance of the flexible board 504 is controlled.
Meanwhile, in an optical component used for transmission of signals with a transmission rate of 16 Gbps, where the flexible board is used for the connection part, “10 Gbit/s Miniature Device Multi Source Agreement (XMD-MSA)” is the standard.
In addition, the following structure has been also suggested. That is, a ground electrode, a signal electrode, and a power source electrode are mounted on the surface of an MIC (Microwave Integrated Circuit) bonded to a base. A ground lead, a signal lead and a power lead are connected by thermo-compression to the corresponding electrodes. On the base, molten resin is dripped over the MIC and hardened to seal the MIC. (See, for example, Japanese Laid-Open Patent Application Publication No. 10-41420).
However, in the example shown in FIG. 4, as the transmission speed is higher such as more than 10 Gbps, it is difficult to secure high frequency properties at a connection part of the IC package 505 and the printed wiring board 6, a connection part of the printed wiring board 6 and the flexible board 504, and a connection part of the flexible board 504 and the optical component 27. Hence, it is necessary to decrease the number of the connection parts.
In particular, in a case of a high speed IC package whereby signals having transmission rate equal to or greater than 40 Gbps can be transmitted, it is preferable to use an IC package having a flexible connection part so that the number of the connection parts is decreased while degradation of the high frequency properties due to the position shift of the printed wiring board 6 and the optical component 27 is prevented.
However, there is no flexible board having good high frequency properties and sealing abilities such as polyimide in the related art. Hence, it is difficult to use the flexible board for the IC package of the compound semiconductor requiring the sealed environment.
In addition, in the example suggested in Japanese Laid-Open Patent Application Publication No. 10-41420, although the flexible board is used as an interposer, the sealing ability of the flexible board itself is low. Hence, a sealable cavity structure is not applied and polyimide resin is used for sealing. Accordingly, high frequency properties of the compound semiconductor cannot be effectively achieved.
In addition, a package has been suggested where a rigid board is used as an interposer and a sealing structure is formed by a lid part made of resin or ceramic so as to form a space inside the lid part. However, in a case of the rigid board unlike the flexible board, the position shift between the printed board 6 and the optical component cannot be cancelled. Hence, it is necessary to connect the flexible board outside the package. Because of this, it is difficult to avoid a problem of degradation of the high frequency properties at the connection part.